Six chimeric bacillary metalloproteinases were purified from culture media of Bacillus subtilis expressing hybrid genes earlier created by homologous recombination. The heat stability and temperature optima were examined for natural secreted metalloproteinases of Bac. amyloliquefaciens and Bac. brevis and their structural hybrids. These experimental data together with the results of computer analysis made it possible to locate additional structural regions essential for the thermal stability of the enzyme molecule as a whole.